Pulse generator



Oct. 30, 1951 M. FISCHMAN 2,573,558

PULSE GENERATOR Filed Oct. 10, 1945 s Sheets-Sheet 1 IlE L 26 mmuumu 5 TE E IHHHHHHI IHIIHIH LIH Oct. 30, 1951 M. FIscI-IMAN 2,573,558

PULSE GENERATOR Filed Oct. 10, 1945 3 Sheets-Sheet 5 26 2 ri 28 :E

+E T I .I. E; 7 O INPuT SIGNAL AT TERMINAL Io TIME I F E, I -IIME: P "TbB%s v aw l E. .L q -figg v OF (8' I I l oEIoNIzATIoNPoTENTIAI.

I OF TUBE v l +5 I I i c o l 'POTENTIAL AT TERMINAL as +E l D l POTENTIALVAT TERMINAL 25 i i 1 TIMI-:--- +E 1 i E POTENTIAL AT CONTROL E l I ELECTRODE OF TUBE v f Y TIME i I' gvwe/wtom E MARTIN FISCHM TIME AN MW W Patented Oct. 30, 1951 UNITED STATE S PATENT OFFICE PULSE GENERATOR Navy I Application October 10, 1945, Serial No. 621,573

' '7 Claims. 1

This invention relates to a pulse generator wherein pulses are formed through the employment of an energy storage device.

More particularly, this invention relates, in general, to a pulse generator of the type wherein the desired pulses are obtained through the periodic charging and discharging of an energystorage device such as a transmission-line section.

Pulse generators are known in the art in which an energy storage device is charged or discharged through a switching means. In such devices the shape of the pulse, particularly the leading and trailing edges, is determined by the characteristics of the energy storage device. Inasmuch as it is diificult to construct a distortionless storage device, pulses whose shape depends on the characteristics of the energy storage device often have long duration leading and trailing edges instead of the sharp discontinuities generally desired.

Accordingly this invention relates to a pulse generator wherein the slope of the trailing edge of a generated pulse is not dependent on the parameters of the transmission-line section which is used, but is determined by auxiliary means which are effective to shorten the duration of the trailing edge.

In the drawings, Figs. 1 to 3, inclusive, represent schematically a balanced transmission-line section or portions thereof and equivalent circuits therefore; Figs. 4 and 5 comprise a series of curves used in explaining the operation of the balanced transmission-line section used in the instant invention; Fig. 6 is a schematic circuit diagram of a pulse generator in accordance with the invention; and Fig. 7 comprises a series of curves used in the explanation of the operation of the Fig. 6 arrangement.

For a better understanding of the operation of a portion of the instant invention, reference is made to Figs. 1 to 5 inclusive, of the attached drawings which illustrate some of the characteristics of a balanced transmission-line section 22.

Referring now more particularly to Fig. 1, there is illustrated the schematic circuit diagram of a balanced artificial transmission-line section 22 which is represented as a four terminal network comprising a pair of parallel-wound inductors A, B, with terminals 23, 24, 25, and 26 as shown. It will be assumed that the network is initially charged to a potential designated E, as shown in Fig. 2, and that an equipotential plane or surface designated P, is disposed intermediate the two windings. This surface represents all points midway in potential between corresponding portions of the two inductors. It is ow of interest to consider the variation, with respect to timefof the potentials of the various terminals when a resistor Z, as shown in Fig. 3, having an impedance equal to the characteristic impedance of the transmission-line section, is connected across terminals 23 and 26. Inasmuch as the load Z is equal in magnitude to the impedance of the line, the potential across the terminals 23 and 26 will drop to one half its original value at the instant of the connection of the load Z. This is represented by the twosteps occurring at time to in the curves of Fig. 4, wherein the curve E23 represents the potential at terminal 23 with respect to the equi-potential plane, and curve E26 represents the potential at terminal 25 with respect to the equipotential plane P. These steps of voltage occurring at time to are propagated down the line toward terminals 24 and 25 where they encounter a discontinuity at the open-circuited end at time t1 and are reflected. This reflection will be of the same polarity as the steps developed at time to, and will arrive at the start-' ing points comprising terminals 23 and 26 at a time t2. It will be seen that the duration of interval to-tz is equal to twice the time required for the translation of a wave signal from one end of the line to the other. The arrival of these reflected wavefronts at the terminals 23 and 26 cause the potential there between to drop to zero at time t2 as shown in curves E23 and E26 of Fig. 4.

Curves E24 and E25 of Fig. 4 represent the potentials which appear across terminals 24 and 25. Prior to the arrival of the voltage step or wavefront from terminals 23 and 26 at time t1, the potential across terminals'24 and 25 has the value E. However, at time t1, the potential across terminals E24 and E25 drops to zero due to the simultaneous presnece of the incident and reflected waves, the sum of which has been shown to be zero.

The above curves represent the voltages at the various terminals with respect to the equipotential surface P. If, however, it is desired to express these voltages with respect to any one of the terminals, it is necessary to add a voltage equal to the voltage originally at the reference terminal to each of the terminals, but in the opposite sense, so that the terminal will correspond, in effect, to the equipotential plane P. Assume, for example, that the terminal 26 of the transmission-line section 22 of Fig. 3 is connected to ground. All voltages may then be conveniently taken with reference to this terminal. By male 3 ing the transformation described above, i, e., by adding a positive vo1tage(-E2s) to each of the curves of Fig. 4, the curves E1a, E'24, E'25, and E26 of Fig. are obtained.

Referring now more particularly to Fig. 6, there is illustrated an input terminal Ill which is connected to the control electrode I3 of a thyratron 'Vi through a condenser II. The control electrode I3 is connected to ground by a resistor I2 and a parallel resistor-condenser combination comprising a resistor I6 and a condenserI I. The junction of resistors I2 and I6 is connected by resistors I4 and I5 to the cathode I9 of thyratron V1, which is in turn connected by a resistor 25 to a source 056 voltage indicated by +'B. An output terminal 33 is also connected to the cathode I9. A condenser I8, the impedance of which is low in comparison to the total resistance of aresistors I5 and I6 is connected between the high potential terminal of resistor I5 and ground. The sum'oi the 'impedances of V1 when conducting, plus resistor I 3., .plus condenser "I8 at the pulse frequencies involved is made equal to the characteristic impedance of line 22. The anode 32 of thyratron V1 is connected by a resistor 'to a source of potential indicated +13, and is directly connected to a terminal 23 of a balanced transmission-line section 22. The anode -3| of a second thyratron V2 is also connected to terminal 23 ofv the transmission-line section, and its cathode 30 is connected to the junction of the resistors I5 and I6. The control electrode 29 of thyratron V2 isconnected through acondenser "2? to a terminal 25 of the transmission-linesection, and is also-connected to ground through a resistor '28 which, with condenser 21, comprises a differentiating circuit. 1

Coming now to the operation of the Fig. 6 arrangement, it is initiallyassumed that the thyratrons V1 and V2 are in a non-conducting state and that the transmission line section 22 has been tullypharged, A positive input pulse-shown as curve A, of .Fig. '7 is then applied to the control electrode I3 of thyratron V1 through the 1 condenser II at time to. This pulse momentarily overcomes the bias created by the voltage divider comprising resistors I 4, I 5, I5, and 20, and causes the-thyratron Vrtoconduct. The relative- 1y low impedance path thus presented across the terminals 23-26 of the transmission-line section 22 allows it to discharge through the resistor I4 and the condenser I8, the reactance of the latter effectively presenting a short-circuit-across the resistors I5 and I6 insofar as the pulse delivered by the transmission-line section is concerned. The decreasein anode potential at-time to'caused by the discharge of the transmission-line section 22 risillustrated by curveZB of Fig. '7. The flow of current through the resistor It causes a voltage drop therein which comprises the leading edge and the constant amplitude portion of the output pulse ofcurve C of Fig. 57 which is delivered to the output terminal 33 between the interval iot1.

At time h, which denotes the end of the delay period to-t1 of the line 22, the voltage at terminal 25 makesva sharp .positive excursion as illustrated .by curve D of .Fig. 7. It will be manifest that this waveshape corresponds to that illustrated-by wave E25 ofFig. '5. 'Thissignal of I curve D is coupled to the control electrode 29 of thyratron'Vz by the differentiating circuit comprising condenser '2! and resistor 28. Theresultant differentiation creates the positive pulse which is illustrated in curveE of Fig. *1 attime t1 and overcomes the bias on thyratron V2, thus causing it to conduct. Because of the fact that the cathodes of thyratrons V1 and V2 are returned to different points on the voltage divider comprising the resistors Id, I5, I5, and 20, the .cathode 30 of thyratron V2 is at a much lower potential than the cathode I9 of thyratron V1. The voltage drop across the anode-cathode circuit of V2, therefore, is sufiiciently low, while it is in a conducting state, that the potential of the anode 3| of thyratron V2, and consequently the anode 32 of thyratron V1, is caused to be at a potential below that of the cathode IQ of thyratron V1. Thyratron V1, therefore, ceases to conduct, and the flow of current from transmission line section 22 through the resistor I4 which comprises the signal delivered to the output terminal 33, ceases abruptly at the time t1 as illustrated in curve C of Fig. I. At time t2, the negative impulse which has been moving down the transmission-linesection 22 arrives at the terminal 23, and this impulse serves to reduce the anode potential of thyratron V2 suificientiyior conduction to cease therein. This is illustrated at time t2 in curve 'B of Fig.7. 'Deionization then taken place, the transmission-line section 22 is charged from the source indicated +B, and the arrangement is then ready to accept a subsequent positive pulse at the input terminal Ill.

Although Ihave shown and described certain specific embodiments of the invention, I'am fully aware of the many modificationsiposs'ible thereof. This invention is not to berestricted except insofar as is necessitated .by prior art and the spirit of the appended claims;

What is claimed is:

1. A circuit for 'generatinga [pulse of predetermined duration comprising the combination of energy storage means having a first terminal, a second terminal, and a third terminal, means connected to said first andsecond terminals effective to charge said energy .storage means, .an impedance .and first switching means connected between said first and said second terminals and efiective to initiate discharge of said energy storage means through said impedance, and second switching means connected between .said first and second terminals and having a control element connected to said third terminal, said second switching means being responsive 'to "signals appearing .onisaid third terminal to remove the potential of the energy storage device from said impedancea predetermined time after initiation of discharge of said .energyst'orage means.

2. A circuit for generating 'a square pulse of predetermined duration comprising in combination an artificial transmission line, means for charging the line, an impedance andi'irst switch tube connected across 'one'end of the line, actuation of said switch'tub'ebeingeiiective to initiate discharge of theline through the "impedance, and a second switch tu'b'e connected a'cross saidone end of the line "and having "a control element .connected 'tothe other end of 'said line, saidfirst and secondswitchtubeshaving a common plate current supply path, whereby a pulse having sharp leading and "trailing edges "is-generated across said impedance.

3. A circuit for generating a square :pulse comprising a'n artificial transmission line, means for chargingthe'lina-an impedance and firstswitc'hing means connected across one end of the line, actuation "of said switching *means being 'e'fiective "to initiate "discharge of the line through the impedance, anda second switching means cennected across said one end of the line and having a control element connected to said other end of the line, whereby a pulse having a width corresponding with the length of the line is generated across the impedance.

4. A circuit for generating a square pulse of predetermined duration comprising in combination an artificial transmission line, means for charging the line, an impedance and first switching means connected across one end of the line, actuation oi said switching means being effective to initiate discharge of the line through the impedance, a differentiating circuit connected to the other end of the line and operative to generate a spike when the reduced voltage caused by connecting the impedance across one end of the charged line travels to the other end of the line, and a second switching means connected across said one end of the line and having a control means connected to said differentiating circuit.

5. A circuit for generating a pulse of predetermined duration comprising the combination of an open-ended transmission line, a source of charging potential connected to one end of said line, a first switching means and an impedance connected in series across said one end of said line, and second switching means connected across said one end of said line and having a control element connected to the other end of said line.

6. A circuit for generating a pulse of predetermined duration comprising the combination of an open-ended transmission line, a source of charging potential connected to one end of said line, a first switching means and an impedance connected in series across said one end of said line, said impedance having a value equivalent to the characteristic impedance of said transmission line, and second switching means connected across said one end of said line and having a control element connected to the other end of said line.

'7. A circuit for generating a pulse of predetermined duration comprising the combination of an open-ended transmission line, a source of charging potential connected to one end of said line, a first switching means and an impedance connected in series across said one end oi. said line, difierentiating means connected to the other end of said line, and second switching means connected across said one end of said line and having a control element connected to said differentiating means.

MARTIN F'ISCHMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number I Name Date 2,405,070 Tonks July 30, 1946 2,511,595 Loughren June 13, 1950 

